This invention relates to dynamoelectric machines such as large generators that have brushes and collector rings located in a movable housing.
In the past, machines have been built with a housing enclosing collector rings and brushes on an extended portion of the rotor shaft. The housing has a closed position with an interface against a fixed wall but can be moved by rolling or sliding to an open position allowing inspection and maintenance of the collector rings and brushes while the machine is in operation. The housing is equipped for forced air cooling that results in a relatively high negative pressure within the housing of, for example, 15 to 20 inches of water. This means that for a typical surface area at the interface of about 3300 sq. in., the direct force required to open the housing while the machine and the ventilation system are in operation is roughly about 2400 lbs. While the actual force required can be reduced by the use of the mechanical advantage of a lever, a prohibitively long lever may be required to achieve sufficient mechanical advantage for a moderate size person to move the housing in a given case.
To avoid the foregoing problems, which is the object of the present invention, there is provided a device to markedly reduce the pressure differential without the exercise of any large manual force. This device, which may be referred to as a "housing access flow control device" or a "vacuum breaker" (since its effect is to relieve the partial vacuum within the housing) is, according to a preferred embodiment of the invention, a portal valve located in a surface of the housing for manual opening prior to the housing being forced away from the interface with the stationary wall. The portal valve may occupy a surface area of the housing that is less than that of the sealed interface by at least about an order of magnitude. Upon its opening, with a manual force of no more than about 15 to 20 pounds, the pressure is relieved and separation at the interface can be readily performed since the force required to pull back the housing is now about 5 to 10% of that required formerly.
The portal valve comprises a pivot plate secured at an edge to a fixed pivot pin. Opposite the fixed pivot pin there is a closure mechanism which may be a screw fastener. The plate has on it a handle for enabling manual rotation of the pivot plate around the pivot pin. Additionally it is preferred that the portal valve have located internally in it a screen to prevent entry of extraneous material as the air pressure within the housing is raised and there is a large inrush from the exterior of the housing.